A　novel　conotoxin,　qc16a,　was　identified　from　the　venom　of　vermivorous　Conus　quercinus.　qc16a　has　only　11　amino　acid　residues,　DCQPCGHNVCC,　with　a　unique　cysteine　pattern.　Its　disulfide　connectivity　was　determined　to　be　I-IV,　II-III.　The　NMR　structure　shows　that　qc16a　adopts　a　ribbon　conformation　with　a　simple　beta-turn　motif　formed　by　residues　Gly6,　His7　and　Asn8.　qc16a　causes　depression　symptom　in　mice　when　injected　intracranially.　Point　mutation　results　showed　that　Asp1,　His7　and　Asn8　are　all　essential　for　the　activity　of　qc16a.　Electrophysiologically,　qc16a　has　no　strong　effect　on　the　whole-cell　currents　of　neurons　and　the　currents　of　Drosophila　Shaker　channels,　human　BK　channels　and　Na(V)1.7　channels.　Its　specific　target　still　remains　to　be　identified.　(C)　2011　Elsevier　Inc.　All　rights　reserved.